When electronic products are becoming smaller in size and more intelligent with a high performance and a high reliability, requirements to integrated circuit (IC) fabrication techniques are accordingly increased for higher integration density of IC.
Among these IC fabrication techniques, lithography process is an important technique used in forming selected circuit patterns on a substrate such as a semiconductor wafer. In general, a photoresist film can be deposited onto the substrate during this process and thereafter pattern-exposed to lithographic equipment in order to transcribe a selected circuit pattern. The photoresist film is subsequently developed with a developer solution to obtain a resist pattern corresponding to the transcribed pattern. The developer is intended to remove the relatively more soluble areas of photoresist, and leave behind the remaining patterned photoresist film, which usually serves as a mask for etching multiple thin film layers on the substrate wafer. Since integration density of IC are increased in fabrication of semiconductor devices, advanced lithography techniques are accordingly required in producing smaller critical dimensions (CDs) and fine patterns including, for example, contact holes having smaller opening sizes or spaces having smaller widths. To fabricate such smaller critical CDs and fine patterns, it is necessary to continually increase patterning resolution in lithography technology.
Because requirement for higher patterning resolution in lithography technology keeps increasing, precise formation of desired pattern profile in the photoresist film on the substrate wafer becomes even challenging and difficult. The process window of formation of desired pattern profile in the photoresist film also becomes more marginal with the more advanced technology node. As such, improvements in tools and methods of the lithography technology continue to be sought.